The field of art to which this invention pertains is the preparation of a cumene feed for a cumene oxidation process. More specifically, the invention relates to a process for the preparation of a cumene feed for cumene oxidation from a fresh cumene stream and a recycle cumene stream containing trace quantities of at least one organic acid compound.
In general, phenols are prepared by the oxidation of a secondary alkylbenzene and the subsequent acid cleavage of the resulting alpha, alphadialkylbenzyl hydroperoxide to form a reaction mixture comprising a phenol, a ketone and unreacted secondary alkylbenzene. The acid cleavage is generally effected in the presence of an aqueous acid catalyst, usually sulfuric acid or sulfur dioxide in aqueous solution, or in the presence of an aqueous hydrochloric or perchloric acid solution. The present invention is particularly directed to a process wherein phenol is prepared by the air oxidation of cumene and the subsequent sulfuric acid cleavage of the resulting cumene hydroperoxide to form a reaction mixture comprising phenol, acetone and unreacted cumene. In addition to the principal products, there are formed varying amounts of by-products such as mesityl oxide, alpha-methylstryrene, p-cumylphenol, phenyldimethylcarbinol, acetophenone, and higher molecular weight phenols.
In the process of recovering phenol from the acid cleavage reaction mixture, the acidic reaction mixture is initially neutralized, either directly by the addition of caustic, or indirectly by contact with an ion exchange resin. In any case, the neutralized reaction mixture is fed to a distillation column, commonly referred to as a crude acetone column, at conditions to effect a crude separation of those materials boiling below phenol whereby an overhead fraction is recovered comprising substantially all of the acetone and lower boiling by-products, as well as a substantial portion of the water and unreacted cumene. Acetone is subsequently recovered, as is cumene, by the further distillation of the crude acetone column overhead. The resulting recovered cumene is recycled to the oxidation process.
The bottoms fraction recovered from the crude acetone column, comprising phenol and alpha-methylstyrene as well as the balance of the water and the bulk of the unreacted cumene, is typically treated for the separation of heavy ends and thereafter fed to a distillation column, commonly referred to as a cumene or alpha-methylstyrene column. The latter column is operated at conditions to separate an overhead fraction comprising water, cumene and alpha-methylstyrene from the higher boiling phenol product. The phenol, recovered as the bottoms fraction, further contains certain impurities, e.g., mesityl oxide and hydroxy acetone, and said impurities are treated and separated from this bottoms fraction to yield a substantially pure phenol product.
The overhead fraction from the cumene column will invariably comprise a significant amount of phenol, between 5 and 25 weight percent, as well as cumene and alpha-methylstyrene. It has been the practice to causticextract this overhead fraction and the cumene and the alpha-methylstyrene recovered as a water-immiscible organic phase is separated and recycled to oxidation as cumene. The phenol is recovered as sodium phenate in the aqueous phase, a practice which has necessitated a separate phenol recovery facility wherein the aqueous sodium phenate solution is acid treated and the resulting sprung phenol being recycled and combined with the acid cleavage product for recovery as hereinabove described, and the acidifying agent being subsequently extracted with a solvent or stripped with stream for economical recovery with phenol, followed by necessary treatment for safe disposal.
The total charge to the oxidation section of a phenol process unit consists of fresh cumene and recycle cumene from other various sections of the unit, i.e., from the spent air treating section, from the concentration section and from the fractionation section. The recycle cumene from the fractionation section normally would have undergone a caustic wash with a 5-30 weight percent caustic solution for the purpose of extracting the phenol and would be basic in nature due to the entrained caustic solution. The cumene recovered from the spent air and from the concentration sections, however, contains small quantities of organic acid compounds which are undesirable in the phenol process unit.
It is therefore necessary to caustic wash the recycle streams and is also desirable to wash the fresh cumene charged to the oxidizer with at least a dilute caustic solution. It is also important that a water wash be performed after the caustic wash in order to remove the entrained caustic since a breakthrough of the caustic to the decomposer would neutralize the small quantity of acid catalyst in the decomposer.
The prior art teaches that the caustic wash and the water wash may be performed in a complex manner and those skilled in the prior art have sought a more efficient process to prepare a cumene feed for cumene oxidation. We have discovered a process for achieving this result which is less complex, more economical and more space efficient.
Previously, it was also advantageous to caustic wash and water wash the oxidizer effluent to remove traces of organic acids, i.e., formic acid, that are formed in the oxidation reaction in order to prevent corrosion in the downstream sections, especially in the fractionation section. In the prior art processes, the waste aqueous phase is normally sent to a cumene extraction column where the cumene hydroperoxide is extracted from the aqueous phase by using a slipstream of the fresh cumene charge which is then sent to the oxidizer. In accordance with the present invention this waste aqueous phase, referred to hereinafter as oxidate wash, is introduced into the countercurrent contacting zone to provide water and to recover trace quantities of cumene hydroperoxide. This eliminates the need for the cumene extraction column and the concomitant expense.
In accordance with the present invention, the total feed caustic and water wash and/or the cumene extraction column is replaced by a single contacter tower as described hereinafter. This single contacter tower is successfully used for both achieving the caustic washing and the subsequent water washing. A process for the preparation of a cumene feed, sufficiently free of phenol, acids and caustic for cumene oxidation which is less complex, more economical and space efficient is disclosed.